The Synthesis of Nano TiO2 Particles Using a DC Transferred Arc Plasma Reactor

137 Pages·2011·3.84 MB·English

The Synthesis of Nano TiO Particles
2
Using a DC Transferred Arc Plasma
Reactor
A Thesis by Xiaohong Liao, B.Sc.

Department of Chemical Engineering
McGill University
Under the Supervision of Prof. Richard.J. Munz

Submitted to the Faculty of Graduate Studies and Research of McGill University in partial
fulfillment of the requirements for the degree of Master in Chemical Engineering

©Xiaohong Liao, April 2011
TO MY MOTHER,
MY HUSBAND,
MY SON,
MY DAUGHTER
AND IN MEMORY OF MY FATHER
Xiaohong Liao, M.Eng. Thesis
ABSTRACT
The effect of quench conditions on the properties of titanium dioxide produced using a
transferred arc process was studied. Rutile phase TiO in the form of micron sized powder was
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decomposed and vaporized in a continuous feed DC transferred arc system. The hot gas stream
exiting the reactor contained a mixture of the decomposition products of titania including
titanium suboxides (TiO, Ti O ), argon (Ar), and oxygen (O ). Rapid quenching of this gas
2 3 2
stream with dry air resulted in the production of a titania aerosol. Collection of the product took
place in the filtration system. The quench conditions studied included pre-quench
temperature, T1 , quench rate, R , residence time,  , and operating power, P . The
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characterization of particles includes phase identification, phase content calculation, size
distribution analysis, elemental composition analysis, and morphology examination.
The range of quench conditions studied were as follows, 1300< T1 <1700K,
8000<R <18000K/s, 50<<80ms, 7.6<P <12.0kW. In general, high quench rate produced
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small size and high surface area products. Residence time had no obvious effect on product size
and crystal phase formation. Low operating power produced a high anatase fraction product. In
all cases, spherical particles of a polymorphous mixture of anatase and rutile with no evidence of
sintering were produced. Particle size ranged from less than 10 to 300nm. A representative
sample has the mode of 22.3nm, median of 28.1nm and geometric standard deviation of 1.6nm.
i
RÉSUMÉ
L'effet des conditions de trempe sur les propriétés du dioxyde de titane produit par un
procédé à arc transféré a été étudié. Des poudres de TiO de la phase rutile et de taille
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micrométrique ont été alimentées en continu dans un arc à courant continu (CC), décomposées et
vaporisées. Le flux de gaz chauds sortant du réacteur contenait un mélange de produits de
décomposition : notamment de l'oxyde de titane (TiO), du Ti O , de l'argon (Ar) et de l'oxygène
2 3
(O ). Une trempe rapide de cet écoulement de gaz avec de l'air sec a abouti à la production d'un
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aérosol d'oxyde de titane qui fût ensuite récupéré avec l'aide d'un système de filtration. Les
conditions opératoires étudiées comprenaient la température initiale avant la trempe, T1, la
vitesse de trempe, Rq, le temps de résidence, , et la puissance de l'arc, Ptorch. La phase, la
teneur de la phase, la distribution de taille, la composition élémentaire ainsi que la morphologie
des poudres produites ont été obtenus.
La gamme de conditions de trempe étudiées était la suivante : 1300 <T1<1700 K, 8000
<R <18000 K/s, 50 <<80 ms, 7.6 <P <12.0 kW. En général, les taux de trempe élevés ont
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généré des poudres de petite taille et surface spécifique élevée. Le temps de résidence n'a eu
aucun effet évident sur la taille des poucres ainsi que sur la formation de la phase cristalline. Une
faible puissance d'opération de la torche mène à la formation de poudres ayant une forte
proportion de la phase anatase. Dans tous les cas, des poudres sphériques constituées d'un
mélange polymorphe d'anatase et de rutile, sans apparence de frittage, ont été produites. La taille
charactéristique des poudres varie de 10 à 300 nm. Un échantillon représentatif a montré un
mode de 22.3 nm, une médiane de 28.1 nm et une écart type géométrique de 1.6 nm.
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Xiaohong Liao, M.Eng. Thesis
ACKNOWLEDGMENTS
First and foremost I want to thank my supervisor Prof. Richard Munz. It has been an
honor to be his last master student. I hope he will enjoy the retirement life as he enjoys helping
his students fulfill their potential as a successful scientist and professor for so many years. He
has taught me, both consciously and un-consciously, how good research is done. I very much
appreciate all his contributions of time, ideas and funding to make my M.Eng. experience
productive and stimulating. The joy and enthusiasm he has for his research was contagious and
motivational for me, even during tough times in the M.Eng. pursuit.
The members of the Munz group have contributed immensely to my personal and
professional time at McGill. I am especially grateful to visiting scholar Dr. J.-W. Wang for his
assistance of the experiments and for the preparation of TiO pellets by his research group in
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China. I appreciate to M.Eng. R. Pristavita and Dr. F. Marion for their advice and helpful insight
on many of the problems encountered during this study. I would like thanks summer student F.
Imami who worked with us.
I would like to acknowledge McGill technicians Dr. X.-D. Liu, M. Riendeau, H.
Campbell, L. Mongeon for the trainings on TEM, XRD, SEM and SEM-EDS analysis,
respectively; and R. Roy, A. Golsztain for their help in the characterization of the titanium
dioxide powder.
I would like to thank the members of the Chemical Engineering non-academic staff, in
particular to L. Cusmich, F. Caporuscio, L. Miller-Aspin, E. Musqrave, J.A. Gadsby, and M.
Gorman.
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I also extend my thanks to N. Mendoza and Dr. S. Coulombe for helping me with the
French translation of the Abstract.
I want to thank the Natural Sciences and Engineering Research Council (NSERC) for
their contribution via the Collaborative Research and Development grant. For my scholarships, I
want to thank the Department of Chemical Engineering of McGill University for the Eugenie
Ulmer Lamother Award and Graduate school of McGill University for the McGill Provost's
Graduate Fellowship.
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Xiaohong Liao, M.Eng. Thesis
TABLE OF CONTENTS
ABSTRACT ..................................................................................................................................... i
RÉSUMÉ ........................................................................................................................................ ii
ACKNOWLEDGMENTS ............................................................................................................. iii
TABLE OF CONTENTS ................................................................................................................ v
LIST OF FIGURES ...................................................................................................................... vii
LIST OF TABLES ......................................................................................................................... xi
NOMENCLATURE ..................................................................................................................... xii
Chapter 1 Introduction ............................................................................................................... 1
1.1 Properties of Nano Titania ................................................................................. 2
1.2 Titania Photo Catalytic Activity ........................................................................ 3
1.3 Objectives .......................................................................................................... 5
Chapter 2 Literature Review..................................................................................................... 7
2.1 Sol-Gel Process.................................................................................................. 7
2.2 Flame Hydrolysis Process ................................................................................. 9
2.3 Plasma Process ................................................................................................ 10
Chapter 3 Apparatus ................................................................................................................ 20
3.1 Plasma Reactor ................................................................................................ 20
3.2 Measurement Techniques and Instrumentation ............................................... 28
Chapter 4 Experimental Procedure .......................................................................................... 31
4.1 Material ............................................................................................................ 31
4.2 Preparation of Reactor ..................................................................................... 31
4.3 Experiments ..................................................................................................... 31
Chapter 5 Analytical Methods ................................................................................................. 33
5.1 Instrumental Analysis ...................................................................................... 33
5.2 Calculation of Operating Parameters ............................................................... 38
Chapter 6 Results and Discussion .......................................................................................... 43
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6.0 Summary of Experimental Conditions ............................................................ 43
6.1 General Observations and Discussion ............................................................. 45
6.2 Experimental Problems.................................................................................... 50
6.3 Product Characterization ................................................................................. 53
Chapter 7 Conclusions ............................................................................................................. 84
Chapter 8 Suggestions for Future Work .................................................................................. 86
REFERENCES ............................................................................................................................. 88
APPENDIX ................................................................................................................................... 95
Appendix A: XRD Phase Identification .................................................................................... 95
Appendix B: SEM-EDS Analysis ............................................................................................. 97
Appendix C: Temperature Profile of the Experiment ............................................................. 104
Appendix D: Experimental Procedure .................................................................................... 106
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LIST OF FIGURES
Figure 1: Crystalline structure of rutile and anatase (Gaffet, 2007). .............................................. 1
Figure 2: Comparison of fumed and precipitated TiO powder by TEM analysis (Bankmann, et
2
al., 1992) ......................................................................................................................................... 4
Figure 3: Schematic diagram for the synthesis of TiO powder by a sol-gel method .................... 8
2
Figure 4: The basic steps of particle formation and growth by gas-to particle conversion adapted
from (Pratsinis, 1998) ..................................................................................................................... 9
Figure 5: Classification of plasmas. .............................................................................................. 11
Figure 6: Transferred arc configuration (left) and non-transferred arc configuration (right) ....... 13
Figure 7: The experimental setups for transverse injection (a) and counter-flow injection (b) of
quench gases (Li, et al., 2007) ...................................................................................................... 16
Figure 8: Drawing of the basic reactor, where segmented torch is connected to the injection-
section, nozzle combination (Kakati, et al., 2007) ........................................................................ 17
Figure 9: Transferred arc plasma reactor configuration (Addona, 1993) ..................................... 21
Figure 10: Transferred arc plasma reactor cut view (Altenhoff, 2009) ........................................ 23
Figure 11: Torch assembly............................................................................................................ 24
Figure 12: Arc ignition and transfer arc system; the upper drawing is for ignition while the lower
is for transferred arc operation (Addona, 1993) ............................................................................ 25
Figure 13: Schematic drawing of the filter baghouse.. ................................................................. 26
Figure 14: Filter cartridge and retainer disc of Model 30 housing (Dow11). ............................... 27
Figure 15: Terminal assignment of I-7019R model (Use11). ....................................................... 29
Figure 16: TriStar 3000 surface area and porosimetry analyzer (Adapted from micromeritics
home page). ................................................................................................................................... 36
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Figure 17: The schematic outline of a TEM (Pri11). .................................................................... 38
Figure 18: Schematic drawing identifying the sites of pressure and temperature measurement in
the plasma rector system. .............................................................................................................. 39
Figure 19: Calibration curve for anatase and rutile ratio calculation. ........................................... 42
Figure 20: System operating power versus pre-quench temperature. ........................................... 48
Figure 21: Crucible and chamber after experiment xl-19. ............................................................ 49
Figure 22: Crucible and chamber after 5 min reaction without feeding. ...................................... 52
Figure 23: XRD spectra of products compared with P25. ............................................................ 55
Figure 24: Peak list of powder produced in run xl-19 with reference peak list of anatase and
rutile. ............................................................................................................................................. 56
Figure 25: Peak list of powder produced in run xl-17 with reference peak list of anatase, rutile
and graphite. .................................................................................................................................. 56
Figure 26: Average crystallite sizes calculated from XRD spectra with the error bars based on
standard deviation. ........................................................................................................................ 58
Figure 27: Crystallite size of the samples versus quench rate with geometric standard deviation.
....................................................................................................................................................... 60
Figure 28: Average particle size based on BET measurement with deviation (sum of
measurement error and geometric standard deviation). ................................................................ 62
Figure 29: TEM images used for particle size calculation (a)Mag. 122 000X (b)Mag. 162 000X.
....................................................................................................................................................... 63
Figure 30: Size distribution histogram of titania particle obtained from TEM with the lognormal
fitting and the corresponding cumulative distribution function. ................................................... 64
Figure 31: SEM images of representative runs (Mag. 50 000 X). ................................................ 66
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